Method of forming a body frame structure for a four-wheeled buggy

ABSTRACT

A body frame structure for a four-wheeled buggy which is constructed by separately preparing the front sub-assembly and the rear sub-assembly and fastening the rear sub-assembly to the front sub-assembly. The front sub-assembly is composed of a pair of sub-assembly parts each of which is formed as an approximate loop shape including a main frame, a front down frame, a lower frame, and a center frame. Rear ends of the main frames are welded to upper ends of the center frames via a cross pipe. Brackets are provided on upper portions of the center frames in such a manner as to extend upwardly therefrom. Upper fastening portions provided at front ends of seat rails constituting part of the rear sub-assembly are fastened to mounting holes formed in the brackets. Stays are provided on lower portions of the center frames, and lower fastening portions provided at front ends of right and left back stays are fastened to the stays. With this configuration, since the stays and the brackets are provided on the same members, that is, the center frames, even if the front sub-assembly is previously constructed by welding, it is possible to prevent deviation in dimensional accuracy of portions of the front sub-assembly  1  to which the rear sub-assembly  2  is to be fastened.

This is a divisional of application Ser. No. 09/354,905, filed Jul. 16,1999, now U.S. Pat. No. 6,412,856.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a body frame structure for afour-wheeled buggy.

2. Description of the Related Art

Japanese Patent Publication No. Hei 7-41861 discloses a body frame for afour-wheeled buggy. The body frame is constructed by separatelypreparing a front body frame for supporting an engine, and a sub-frame(rear body frame) for supporting a load-carrying platform. Upperfastening portions are provided on seat rails and back tubes of thesub-frame for obliquely connecting the seat rails to lower framespassing under the engine.

In the above structure, the upper and lower fastening portions providedon the sub-frame are fastened to the seat rails and the back tubes.Accordingly, if the body frame is constructed by welding the front bodyframe, such as the back tubes and the seat rails to each other, thenwhen fastening the sub-frame to the front body frame, the dimensions ofthe seat rails and the back tubes to which the upper and lower fasteningportions are to be fastened, may deviate due to the welding of the backtubes to the seat rails. This makes it difficult to maintain dimensionalaccuracy of the portions of the seat rails and the back tubes to whichthe upper and lower fastening portions are to be mounted and hence toreadily assemble the sub-frame to the front body frame.

To solve such a difficulty in constructing the body frame by fasteningthe sub-frame to the already assembled front body frame, the body framemust be constructed by fastening the seat rails and the back tubes tothe sub-frame before welding the back tubes to the seat rails. The frontbody frame is then constructed by welding components such as the backtubes and the seat rails to each other.

However, in the above-described assembling process, since thelarge-sized members, which are substantially comparable to the bodyframe, must be assembled by welding, the handling performance isdegraded and the assembling efficiency is significantly reduced.Accordingly, it is desirable to separately sub-assemble the front bodyframe and the rear body frame and then fasten the sub-assemblies to eachother in order to construct the body frame.

Further, the body frame is required to have a high rigidity against atransverse load applied to the seat rails. That is, high transverserigidity is required when the body frame is used with a four-wheeledbuggy of the type including two front wheels and two rear wheels,wherein the rear wheels are supported via a common axle on the right andleft sides of a rear end of a rear swing arm with its front endswingably supported to a vehicular body. To be more specific, for such afour-wheeled buggy of this type, a torsional force is applied to avehicular body when the buggy is turned, and even during usual runningwith no turning, a torsional force is also applied to the vehicular bodydue to a difference in height between the two rear wheels when the buggyruns on irregular road surfaces. As a result, the vehicular body of thefour-wheeled buggy of this type, particularly, a sport buggy is requiredto have a transverse rigidity much larger than that of a saddle typemotorcycle.

SUMMARY OF THE INVENTION

To solve the above-described problems, according to the presentinvention, there is provided a body frame structure for a four-wheeledbuggy of a type which includes two front wheels and two rear wheels, therear wheels being supported via a common axle on right and left sides ofa rear end of a rear swing arm with its front end swingably supported bya vehicular body, the body frame structure including: a front body framefor supporting an engine, and a rear body frame for supporting a seat,the front body frame and the rear body frame being previouslyconstructed into different sub-assemblies and then fastened to eachother into one-body; wherein the front body frame includes a pair ofright and left main frames extending in the longitudinal direction whilepassing above the engine, and a pair of right and left center framesextending downwardly from rear ends of the main frames while passingbehind the engine, and the rear body frame includes a pair of right andleft seat rails for supporting a saddle type seat, a pair of right andleft upper fastening portions provided at front ends of the seat rails,and a pair of right and left lower fastening portions provided under theupper fastening portions; and wherein the right and left upper fasteningportions are connected to each other with a cross member, and the rightupper fastening portion and the right lower fastening portion arecommonly fastened to the right center frame and the left upper fasteningportion and the left lower fastening portion are commonly fastened tothe left center frame.

With this configuration, since the portions, to which the upper andlower fastening portions of the rear body frame are to be mounted, areformed on the same members, that is, the center frames, the upper andlower fastening portions of the rear body frame can be fastened to thesame members, as opposed to different members as is conventionallyknown. Accordingly, even if the main frames are welded to the centerframes to sub-assemble the front body frame before the rear body frameis fastened to the front body frame, it is possible to keep dimensionalaccuracy between the portions to which the upper and lower fasteningportions are to be fastened, without being adversely affected by thewelding process.

As a result, the work of constructing the body frame can be facilitatedby separately sub-assembling the front body frame and the rear bodyframe, and constructing the body frame by integrally fastening thesub-assemblies to each other.

Also, since the upper fastening portions provided at the right and leftfront ends of the seat rails are connected to each other with the crossmember, it is possible to ensure the strength of the upper fasteningportions, and hence to increase the transverse rigidity of the bodyframe. Accordingly, the body frame having such a high transverserigidity can be suitably used for a four-wheeled buggy of a typeincluding two front wheels and two rear wheels, wherein the rear wheelsare supported via a common axle on the right and left sides of a rearend of a rear swing arm with its front end swingably supported by avehicular body. The body frame is also applicable to a sport buggy whichparticularly requires a high transverse rigidity.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a side view illustrating a body frame according to anembodiment of the present invention;

FIG. 2 is a side view showing an entire configuration of an essentialportion of a vehicular body;

FIG. 3 is a plan view of FIG. 2;

FIG. 4 is an enlarged side view showing a rear portion of a front bodyframe;

FIG. 5 is a rear view of the front body frame; and

FIG. 6 is a plan view of seat rails according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, one embodiment in which the present invention is applied toa four-wheeled buggy will be described with reference to the drawings.

As shown in FIGS. 1 to 3, a body frame according to this embodiment isconstructed by preparing a front sub-assembly 1 constituting a frontbody frame and a rear sub-assembly 2 constituting a rear body frame, andfastening the rear sub-assembly 2 to the front sub-assembly 1.

The front sub-assembly 1 for supporting an engine 7 is composed of apair of right and left sub-assembly parts each of which is formed as anapproximate loop shape as seen from a side view and which includes amain frame 3, a front down frame 4, a lower frame 5, and a center frame6.

The main frame 3 extends in the longitudinal direction while passingabove the engine 7. The front down frame 4 is continuous to a front endof the main frame 3 in such a manner as to extend forwardly, obliquelydownwardly therefrom. A lower end of the front down frame 4 is welded toa front portion of a reinforcing member 8 extending obliquely upwardlyfrom the lower frame 5.

A front end of the reinforcing member 8 is connected to a front end ofthe lower frame 5 with a front pipe 9. An intermediate portion of thereinforcing member 8 is connected to an intermediate portion of thelower frame 5 with an intermediate pipe 10. Under the engine 7, a rearend of the reinforcing member 8 is directly welded to a portion behindthe intermediate portion of the lower frame 5. Connecting brackets 11and 12 for upper and lower arms (not shown) constituting a doublewishbone type suspension for suspending front wheels 13 are provided onthe reinforcing members 8 and the lower frame 5, respectively. To bemore specific, two pieces of each of the brackets 11 are located on eachreinforcing member 8 at positions spaced in the longitudinal direction,and two pieces of the brackets 12 are located on each lower frame 5 atthe corresponding positions spaced in the longitudinal direction.

A bumper 14 is connected to the front ends of the right and leftreinforcing members 8 and to the right and left lower frames 5. A stay15 for supporting an upper end of a damper (not shown) of a frontsuspension is hung between the vicinities of the right and left curvedboundaries between the right and left main frames 3 and the right andleft front down tubes 4.

A reinforcing pipe 16 extends obliquely rearwardly and downwardly from aportion, in the vicinity of the stay 15 of each main frame 3, to aportion connected to the intermediate pipe 10 of each reinforcing member8. An oil tank 17 is supported by the right and left reinforcing pipes16. The oil tank 17 positioned in front of the engine 7 is surrounded bythe right and left reinforcing pipes 16, the right and left reinforcingmembers 8, the right and left lower frames 5, and the like, and isconnected to an oil cooler 19 via a tube 18. The oil cooler 19 issuspended from portions of the main frames 3 and positioned above theoil tank 17.

A steering shaft 21 supporting stay 20 is provided on portions at themain frames 3, in the vicinity of the oil cooler 19, and the steeringshaft 21 is turnably supported by the stay 20. A handlebar 22 is mountedon an upper end of the steering shaft 21. A lower end of the steeringshaft 21 is supported by bearing portions 23 provided on the lowerframes 5. One end of a tie rod (not shown) is connected to a portionnear the bearing portion 23.

In the figures, reference numerals 24 and 25 designate engine hangersprovided on the lower frame 5; an exhaust pipe 26; a carburetor 27; anda muffler 28 are also shown. In FIG. 5, reference numeral 29 designatesa cross pipe for connecting lower ends of the right and left centerframes 6 to each other; 29 a is a link bracket provided at anintermediate portion of the cross pipe 29; and 29 b is a link arm for arear wheel suspension to be described later.

A rear end of the lower frame 5 extends rearwardly while passing underthe engine 7, being bent upwardly in the vicinity of a rear end of theengine 7, and is continuous to the center frame 6.

A pivot plate 30 is welded to the front side of a lower portion of thecenter frame 6. A front end of a rear swing arm 32 is swingablyconnected to the center frames 6 via a pivot 31 mounted to the right andleft pivot plates 30. The rear swing arm 32 extends rearwardly from thepivot 31, and rear wheels 33 are supported by a common axle 33 a on theright and left sides of a rear end of the rear swing arm 32. A damper 34for the rear wheel suspension is provided between the rear swing arm 32and the front sub-assembly 1.

A stay 35, which constitutes a lower connecting portion as a matingportion with which the rear sub-assembly 2 is to be fastened, isprovided on the back side of the center frame 6 at a position near thepivot 31. That is a stay 35 is positioned on a bottom end 6 b of each ofthe center frames 6. A bracket 36, which constitutes an upper connectingportion as a mating portion with which the rear sub-assembly 2 is to befastened, is provided in such a manner as to extend upwardly from theupper end of the center frame 6. As shown in FIG. 4, the upper endportion of the bracket 36 has mounting holes 37.

As shown in FIGS. 3 to 5, the rear ends of the main frames 3 are weldedto the upper ends of the center frames 6 with a cross pipe 38. To bemore specific, the cross pipe 38 is provided transversely in the widthdirection of the vehicular body, and the rear ends of the right and leftmain frames 3 are welded to the front sides of the right and left endsof the cross pipe 38, and the upper ends of the right and left centerframes 6 are welded to the lower sides of the right and left ends of thecross pipe 38. Both ends of the cross pipe 38 are butted and welded tothe inner sides of central portions of the brackets 36 projectingupwardly from the right and left center frames 6. A cushion bracket 39for supporting the upper end of the damper 34 extends rearwardly from anintermediate portion of the cross pipe 38.

The rear sub-assembly 2 includes right and left seat rails 40, and apair of right and left back stays 41 provided under the seat rails 40 insuch a manner as to extend downwardly and forwardly, and are slightlyspread to the right and left. The right and left back stays 41 areformed into asymmetric shapes. Front ends of the right and left seatrails 40 are connected to a pipe-like cross member 42. Right and leftends of the cross member 42 constitute upper fastening portions 43 whichare to be fastened to the mounting holes 37 of the brackets 36 withbolts. Corner portions at which the cross member 42 is connected to theright and left seat rails 40 are reinforced by corner plates 44 whichare welded to the cross member 42 and the seat rails 40. Intermediateportions of the right and left seat rails 40 are connected to each otherwith a cross plate 45, and rear ends of the right and left seat rails 40are continuously connected to each other. The seat rails 40 areconnected to the back stays 41 with a reinforcing member 46.

Plate-like lower fastening portions 47 are provided at front ends of theright and left back stays 41, and have through-holes 48. The lowerfastening portions 47 are fastened to the stays 35 with bolts passingthrough the through-holes 48 and the mounting holes 35 a of the stays 35(see FIG. 4).

The function of the embodiment will be described hereinafter. The bodyframe is constructed in accordance with the following procedure. First,as shown in FIG. 1, the front sub-assembly 1 and the rear sub-assembly 2are separately constructed by, for example welding. Then, the upperfastening portions 43 provided at both ends of the cross member 42 ofthe rear sub-assembly 2 are inserted between the right and left brackets36 of the front sub-assembly 1, being aligned with the mounting holes 37of the brackets 36, and fastened thereto with the bolts.

The lower fastening portions 47 of the right and left stays 41 areoverlapped to the stays 35, and are fastened thereto with the boltspassing through the through-holes 48 of the lower fastening portions 47and the through-holes 35 a of the stays 35. In this way, the frontsub-assembly 1 is integrally fastened to the rear sub-assembly 2, toconstruct the body frame of the embodiment shown.

In this case, since the stays 35 and the brackets 36 are welded to thecenter frames 6 as common members, even if the main frames 3 are weldedto the center frames 6 to construct the front sub-assembly 1, thereoccurs no dimensional deviation between the stays 35 and the brackets36, thereby preventing deviation in dimensional accuracy of the portionsof the front sub-assembly 1 to which the rear sub-assembly 2 is to befastened.

Accordingly, since the front sub-assembly 1 can be previouslyconstructed by welding the relatively small-sized components before therear sub-assembly 2 is fastened to the front sub-assembly 1, it ispossible to improve the handling performance upon construction of thefront sub-assembly 1, and hence to facilitate the ease of constructingof the entire body frame.

Also since the right and left seat rails 40 are connected to each otherwith the cross member 42 and the upper fastening portions 43 areprovided at both ends of the cross member 42, it is possible tosufficiently ensure the strength of the upper fastening portions 43 andalso to increase the transverse rigidity of the fastening portions ofthe seat rails 40. The body frame having such a high transverse rigiditycan be suitably used for a four-wheeled buggy of a type including thetwo front wheels 13 and the two rear wheels 33 wherein the rear wheels33 are supported via the common axle 33 a on the right and left sides ofthe rear end of the rear swing arm 32, and also applicable to a sportbuggy which particularly requires a high transverse rigidity.

Further, as is apparent from FIG. 2, since the oil tank 17 is disposedunder a portion connected to the exhaust pipe 26 of the engine 7, it ispossible to allow running wind to be sufficiently contact with acylinder head of the engine 7 and the exhaust pipe 27, and hence to keepa high cooling efficiency for these parts. In addition, the arrangementposition of the oil tank 17 with respect to the engine 7 is not limitedto that described in the embodiment. For example, the oil tank 17 may beoffset upwardly or rightwardly or leftwardly from the portion, connectedto the exhaust pipe 26, of the engine 7.

The present invention is not limited to the above embodiment, and can bevariously modified. For example, the pair of right and left main framesand the pair of right and left center frames constituting part of thefront body frame may be replaced with a single main frame and a singlecenter frame, respectively. In the case of the single center frame, thefastening portions of the rear body frames are fastened to the singlecenter frame as the common mounting member.

The rear body frame may include an article supporting member such as aload-supporting platform insofar as it includes the seat rails. Further,the present invention can be applied to a saddle type vehicle such as athree-wheeled buggy or a motorcycle.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

We claim:
 1. A method for forming a contiguous body frame, the methodcomprising: separately constructing a front body frame and a rear bodyframe sub-assembly, said front body frame including a main frameextending in a longitudinal direction of said contiguous body frame;inserting upper fastening portions provided at both ends of a crossmember of the rear frame sub-assembly between right and left brackets ofthe front assembly; aligning mounting holes of the right and leftbrackets with the upper fastening portions; inserting a plurality ofbolts through the mounting holes to fasten the front and rear frameassemblies together; overlapping stays of the rear frame sub-assemblywith stays of the front sub-assembly; and inserting a plurality of boltsthrough through-holes of lower fastening members of the stays of therear frame sub-assembly and through-holes of the stays of the front subassembly to further fasten the front and rear frame assemblies together.2. A method for forming a contiguous body frame for a vehicle, said bodyframe structure for the vehicle including a front body frame; and a rearbody frame, the rear body frame being fastened to the front body frame,wherein the front body frame includes first and second upper main framesextending longitudinally, first and second lower frames extendinglongitudinally, a cross pipe attached to a distal end of each of thefirst and second upper main frames, first and second center framesextending obliquely from the cross pipe, and first and second bracketsattached to the cross pipe, each of the first and second bracketsreceiving a portion of the rear body frame to thereby fasten the rearbody frame to the front body frame, wherein the front body frame furtherincludes a stay attached to each of the first and second center frames,each of the stays receiving a portion of the rear body frame, whereineach of said stays and each of said brackets is respectively welded tosaid first and second center frame to prevent a deviation in dimensionalaccuracy, said method comprising: separately constructing the front andthe rear frame as a front sub-assembly and a rear sub-assembly;inserting upper fastening portions provided at both ends of a crossmember of the rear frame sub-assembly between the first and the secondbrackets of the front assembly; aligning mounting holes of the first andthe second brackets with the upper fastening portions; inserting aplurality of bolts through the mounting holes to fasten the front andthe rear frame assemblies together; overlapping stays of the rear framesub-assembly with the stays of the front sub-assembly; and inserting aplurality of bolts through through-holes of lower fastening members ofthe stays of the rear frame sub-assembly and through-holes of the staysof the front sub assembly to further fasten the front and rear frameassemblies together.
 3. A method for forming a contiguous body frame fora vehicle, said body frame structure including a front body frame; and arear body frame, the rear body frame being fastened to the front bodyframe, wherein the front body frame includes first and second upper mainframes extending longitudinally, first and second lower frames extendinglongitudinally, a cross pipe attached to a distal end of each of thefirst and second upper main frames, first and second center framesextending obliquely from the cross pipe, and first and second bracketsattached to the cross pipe, each of the first and second bracketsreceiving a portion of the rear body frame to thereby fasten the rearbody frame to the front body frame, wherein the first and secondbrackets are attached to the cross pipe at first and second distal endsthereof, respectively, said method comprising: constructing the frontand the rear frame as a separate front sub-assembly and a separate rearsub-assembly; inserting upper fastening portions provided at both endsof a cross member of the rear frame sub-assembly between the first andthe second brackets of the front assembly; aligning mounting holes ofthe first and the second brackets with the upper fastening portions;inserting a plurality of bolts through the mounting holes to fasten thefront and the rear frame assemblies together; overlapping stays of therear frame sub-assembly with the stays of the front sub-assembly; andinserting a plurality of bolts through through-holes of lower fasteningmembers of the stays of the rear frame sub-assembly and through-holes ofthe stays of the front sub assembly to further fasten the front and rearframe assemblies together.
 4. The method according to claim 2, furthercomprising attaching the first and second brackets to the first andsecond center frames, respectively.
 5. The method according to claim 2,providing a cushion bracket for the front body frame attached to anintermediate portion of the cross pipe.
 6. The method according to claim2, further comprising: attaching the first and the second upper mainframes to a first transverse portion of the cross pipe; and attachingthe first and second center frames to a second transverse portion of thecross pipe, wherein the first and second transverse portions do notoverlap.
 7. The method according to claim 2, further comprising:attaching the first distal end to an interior facing central portion ofthe first bracket; and attaching the second distal end to an interiorfacing central portion of the second bracket.